Teach me about the idle circuit
 

so, first off I have an 83 gs with a fresh motor and full racing beat exhaust. The car is new to me. I rebuilt the carb and stripped it of all the emissions crap. I retained the choke flap but cleaned up the top of the carb and converted it to mechanical secondaries. The a/p mod has been done too. The motor has the rats nest removed and the valve in the intake removed as well. Holes have been filled with jb weld. All jetting is stock in the carb.

Here is the problem. I have to run my idle mixture screw out 6 turns to get the car to idle. It's still not a perfectly smooth idle either. The car runs fantastic through the rpm range with the exception of just off idle cruising. It surges a little then. Then when starting the motor hot it struggles big time. There are NO vacuum leaks. I've searched for them many times thinking that's the problem. So, is there an idle feed restriction in the carb? I know it gets it's fuel from the main jet and I know it has idle air bleeds. I'm trying to figure out why i have to have the mixture screw out so far and why it is hard to start when hot.

Oh, the car has a Holley fuel pump with a regulator and set to 3psi.

Stock fuel pressure is 3.5 PSI if not mistaken. However do not think this is causing your issue.


There are two screws that you adjust, one is mixture and one is idle speed. When I put my RB full system in had to adjust both slightly. Method that worked for me was to set the idle speed to 750/800 RPM, then back mixture down until car stumbles then open up until it idles smoothly. I had to play with both (only slightly) for a few days then it was fine.

Yes, I understand there are two screws. I'm just trying to figure out why my mixture screw has to be so far out. If someone has a diagram of the idle circuit so I could make sure mine is clear that would be great. The thing that bothers me the most is the hot start issue.

So I tore the carb back down and traced the idle circuit back from the transfer slots. They run through the throttle body, into the main body and to the idle air bleed hole. It gets it's fuel from the next hole over that has the emulsifying tube (which is fed from the primary main jet). There is a little hole between the two with a small hole that's not reachable. The most we can do is make sure it is clean and clear.

you can also replace the idle air bleeds with smaller ones to boost the circuit signal/strength...

I ended up soldering the air bleeds shut and drilled them the next size smaller. I can't remember the drill bit size I used. I'm going to go another size smaller. They started life as a 180.

OP you should read the Mazda carb training manual. Go to foxed.CA, under rx-7 manuals, subsection other manuals.